Streamer cable with enhanced properties

ABSTRACT

The present invention relates to streamer cables. One embodiment of the present invention relates to a method for preparing a streamer cable. The method may comprise retrofitting the streamer cable with a solid void-filler material, where the streamer cable was configured as a liquid-filled streamer cable. The retrofitting may comprise introducing a void-filler material into the streamer cable when the void-filler material is in a liquid state and curing or otherwise solidifying the void-filler material to a solid state. In another embodiment, the present invention relates to a streamer cable comprising an outer skin and-at least one sensor positioned within the outer skin. The streamer cable may also comprise a solid void-filler material positioned between the outer skin and the at least one sensor, wherein the solid void-filler material is coupled to the at least one sensor.

FIELD OF TECHNOLOGY

This invention relates to improvements to streamer cables, and methodsof retrofitting and producing streamer cables. More specifically, theinvention relates to streamer cables with solid void-filler materials,and methods of retrofitting streamer cables configured as liquid-filledstreamer cables with a solid void-filler material.

BACKGROUND OF THE TECHNOLOGY

Streamer cables are used in a variety of applications, usually involvingremote sensing in water environments, for example, in fresh or saltwaterbodies. The cables are typically used for seismic exploration surveys togather information about subsurface geology, including oil and gasreserves. The cables usually contain one or more sensors for receivingsignals present in the water. Often, the sensors include hydrophones forsensing acoustic signals. Individual streamer cables are often made upof a series of sections, which may be on the order of 75 meters long. Indeployment, streamer cables, or arrays of several streamer cables, maybe towed behind vessels, or deposited at fixed locations, such as oceanfloor locations.

In a typical seismic exploration survey, one or more streamer cables aretowed behind a tow vessel. The one or more streamer cables often form anarray that may include a dozen or more parallel cables, each manykilometers in length. The tow vessel, or another vessel, may include anacoustic source for generating acoustic signals. The acoustic signalspropagate through the water and interact with various structures in thewater, on the ocean floor, and/or below the ocean floor. Theinteractions may produce reflections and/or refractions that may besensed by the streamer cables and used to generate information about thereflecting or refracting structures. For example, an energy company maybe able to locate areas beneath the ocean floor that are more likely tocontain deposits of oil, gas and/or other minerals by examining theinformation developed from the acoustic reflections and/or refractionsreceived by hydrophone sensors contained within a streamer cable. Oftenthe acoustic signals used in seismic surveys are of a very lowfrequency, for example, between 3 and 150 Hz.

Streamer cables may also be used in other applications, such assurveillance applications. In some applications, one or more streamercables are referred to as towed arrays. In an example surveillanceapplication, a military vessel may tow or deposit a streamer cablecontaining sensors capable of detecting, for example, the noisegenerated by other vessels. Streamer cables in such surveillanceapplications may be capable of sensing acoustic energy over a muchbroader bandwidth than the 3-150 Hz frequency range discussed above.

Conventional streamer cables are liquid-filled. Liquid-filled streamercables typically include an outer skin that houses the components of thecable including, sensors, strength members, wires, etc. After thestreamer cable is configured, a liquid void-filler material, for examplekerosene, is added to fill the void between the outer skin and thesensors, strength members, etc. The liquid void-filler typicallyprovides acoustic coupling between the outer skin and the sensors. Thespecific liquid void filler material may be selected to adjust theoverall density of the streamer cable and therefore affect its buoyancy.

Although they are widely used, liquid-filled streamer cables presentseveral difficulties. First, because the liquid void-filler material maybe mobile within the outer skin, mechanical energy resulting from themovement of the cable, tow vessel, and cable handling devices in thewater may be acoustically coupled to the sensors by bulge waves in thecable. Additionally, the liquid void filler of liquid-filled cables mayleak into the body of water when the outer skin is damaged. A liquidvoid-filler, such as kerosene may create an environmental hazard whenleaked into a body of water. Also, leaked liquid void filler may bereplaced in the streamer cable by water, which can degrade receivedsignals and cause corrosion of the internal components of the streamercable, especially in saltwater environments. As such, many energycompanies and other users of streamer cables have begun to favoralternatives to liquid-filled streamer cables.

Solid streamer cables, i.e. streamer cables with solid void-fillers,have been developed in an attempt to address the problems ofliquid-filled streamer cables. A common type of solid streamer cableincludes a solid central core with sensors, skin, buoyant material, andother various components installed thereabout. Another type of solidstreamer cable includes alternating sections of sensors and buoyantmaterial. As an alternative to liquid-filled cables, solid streamercables have superior leakage and bulge wave reduction qualities, butpresent other difficulties of their own.

For example, solid streamer cables suffer various problems related tobuoyancy. The solid core and other solid materials in the cablestypically have a density greater than that of seawater. Therefore,additional buoyant material, often hollow microbead material made ofglass or foam, is placed in the streamer cable to reduce its overalldensity. Because the density of the microbead material is related to thequantity of air positioned within the microbeads, insuring consistentdensity throughout the microbead material may be costly and complicated.

Also, microbead material made of glass or foam tends to crush whensubjected to excessive force, causing the overall density of thestreamer cable to increase, and causing a loss of buoyancy. For example,if a solid streamer cable is handled roughly, or coiled at a smallradius, microbead material may be crushed. Often tow vessels outfittedto handle and store liquid-filled cables must be refitted with newhandling equipment, including coiling spools, etc., before the vesselsmay safely handle solid cables. Microbead material may also be crushedby water pressure if the streamer cable is operated beyond a certaindepth. In extreme situations, solid cables with crushed microbeadmaterial may lose considerable buoyancy, and sink beyond recovery.

Solid streamer cables also suffer from noise problems due to shear waveenergy. Because the solid materials in existing solid streamer cables,including glass microbead materials, have low compliance, energy fromthe motion of the cable in the water can be coupled through the solidmaterials to the sensors in the form of shear waves. Isolating thesensors from the shear waves presents a considerable challenge. Often,the sensors are placed in a rigid isolation structure or housingembedded in the solid void-filler material. The structure or housing maythen be filled with a liquid void-filler for providing the necessaryacoustic properties and negating the negative properties of the solidvoid-filler. Conventional streamer cables with liquid void-fillermaterial typically do not contain such isolation structures for sensors.It can be appreciated that the necessity of isolating sensors within acable, such as with isolation structures, adds complexity and expense,and also limits the potential configurations of the sensors and types ofsensors that may be installed within the streamer cable.

Repairing existing solid streamer cables may also present certaindifficulties. For example, it may be necessary to remove large sectionsof solid material to access damaged sensors or signal wire. It can beseen that replacing the sections of solid material of existing solidstreamer cables without adversely affecting the signal qualities of thecable presents a considerable challenge.

Accordingly, there is a need for a streamer cable with a void-fillermaterial that remains largely confined to the cable in the event of afailure of the outer skin. Also, there is a need for a solid void-fillermaterial for retrofitting existing liquid-filled streamer cables. Thereis also a need for a streamer cable with a void-filler material thatdoes not couple excessive shear wave or bulge wave energy to the sensorsof a streamer cable.

SUMMARY OF THE INVENTION

One embodiment of the present invention relates to a method forpreparing a streamer cable. The method may comprise retrofitting thestreamer cable with a solid void-filler material, wherein the streamercable was configured as a liquid-filled streamer cable. The retrofittingmay comprise introducing a void-filler material into the streamer cablewhen the void-filler material is in a liquid state and curing orotherwise solidifying the void-filler material to a solid state.

Another embodiment of the present invention relates to a streamer cable.The streamer cable may comprise an outer skin and at least one sensorpositioned within the outer skin. The streamer cable may also comprise asolid void-filler material positioned between the outer skin and the atleast one sensor, wherein the solid void-filler material is coupled tothe at least one sensor.

A further embodiment of the present invention relates to a method forpreparing a streamer cable. The method may comprise introducing anadditive into the streamer cable and introducing a gel concentrate intothe streamer cable. The method may also comprise solidifying the gelconcentrate and the additive.

Yet another embodiment of the present invention relates to a method ofperforming maintenance on a streamer cable. The method may comprisechanging the state of a void-filler material within the streamer cablefrom a solid state to a liquid state and removing a portion of thevoid-filler material from the streamer cable. In various embodiments,the method may also comprise performing a maintenance operation on thestreamer cable, or simply replacing the void-filler material.

A further embodiment of the present invention relates to a method ofpreparing a streamer cable. The method may comprise introducing a voidfiller material into the streamer cable, where the void-filler materialis in a liquid state, and curing the void-filler material to a solidstate.

Unless otherwise indicated, all numbers expressing quantities ofingredients, time, temperatures, and so forth used in the presentspecification and claims are to be understood as being modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and claims are approximations that may vary depending uponthe desired properties sought to be obtained by the present invention.At the very least, and not as an attempt to limit the application of thedoctrine of equivalents to the scope of the claims, each numericalparameter should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques.

The reader will appreciate the foregoing details and advantages of thepresent invention, as well as others, upon consideration of thefollowing detailed description of embodiments of the invention. Thereader also may comprehend such additional details and advantages of thepresent invention upon making and/or using embodiments within thepresent invention.

BRIEF DESCRIPTION OF THE FIGURES

The features and advantages of the present invention may be betterunderstood by reference to the accompanying figures in which:

FIG. 1 is a simplified cross-sectional diagram of a section of streamercable according to various embodiments of the present invention;

FIG. 1A is a diagram of a bulkhead according to various embodiments ofthe present invention;

FIG. 2 is a flow chart of a method for installing void-filler materialinto a streamer cable according to various embodiments of the presentinvention;

FIG. 3 is a flow chart of a method for installing void-filler materialinto a streamer cable according to various embodiments of the presentinvention; and

FIG. 4 is a flow chart of a method for maintaining a streamer cableaccording to various embodiments of the present invention.

DESCRIPTION ON THE INVENTION

Embodiments of the present invention relate to streamer cables, solidvoid-filler material for streamer cables, methods of retrofittingstreamer cables configured for liquid void-filler materials, methods ofmaking streamer cables, and methods of maintaining streamer cables.Embodiments of the apparatus and methods of the present invention maycombine the benefits of existing solid and liquid-filled streamer cablesincluding, for example, minimizing the environmental concerns associatedwith liquid-filled streamer cables, without incorporating all of theproblems of existing solid and liquid-filled streamer cables.

FIG. 1 is a cross-sectional diagram of a section of streamer cable 100according to various embodiments of the present invention. An outer skin102 may enclose the streamer cable 100 and surround the sensors 108 andany other internal components, as discussed below. The outer skin 102may be watertight to prevent outside water from contacting the sensors108 and other components of the streamer cable 100. In variousembodiments, the outer skin 102 may be made of materials known in theart including, for example, polymeric materials. One or more strengthmembers 104 within the outer skin 102 may provide the streamer cable 100with strength as well as secure components at locations within thestreamer cable 100. In various embodiments, strength members 104 may becables made of fiber, synthetic materials, wire, etc.

Sensors 108 may include various kinds of transducers and/or otherinstruments for measuring signals incident on the streamer cable 100. Invarious embodiments, one or more of the sensors 108 may be a hydrophonefor sensing acoustic signals. Other types of sensors 108 may also beused including, for example, directional sensors, magnetic sensors,temperature sensors, pressure sensors, etc. The sensors 108 may transmitreceived signal information according to various transmission methodsincluding, for example, electrical or optical methods. Wires 110 maytransmit the received signal information and may be, for example,electrical signal wires, fiber optic cables, etc.

Sensors 108 may be secured within the streamer cable 100 by mountingmechanisms 122 and/or bulkheads 106, and may be positioned at anypractical interval, position, or orientation within the outer skin 102of the streamer cable 100 including, for example, the positions shown bysensors 108 a, 108 b, and 108 c. Mounting mechanisms 122 may be made ofwire, cable, or any other suitable material and may secure sensors 108 aand 108 b to strength members 104 using tie-wraps, for example. In someembodiments, mounting mechanisms 122 may include a sleeve (not shown)for enclosing the sensors 108 a and 108 b, and may be made of variousmaterials including, for example, plasticized PVC, nylon, etc.

FIG. 1A shows a view of a bulkhead 106 according to various embodimentsof the present invention. The bulkhead 106 may be made of any suitablematerial including, for example, plastic or other suitable material.Cavities 116 in the bulkhead 106 may be used to secure the bulkhead 106to the strength members 104 of the streamer cable 100. Cavity 124 maycontain the wires 110 discussed above. Cavity 118 may house a sensor 108c, with active surfaces 120. Active surfaces 120 may be the portion orportions of a sensor 108 that are sensitive to signals. In variousembodiments, cavity spaces within the bulkhead 106 that are nototherwise filled may include the void-filler material 112.

Referring back to FIG. 1, void-filler material 112 may be positionedbetween the outer skin 102 and the various other components of thestreamer cable 100. The void-filler material 112 may be solid duringoperation of the streamer cable 100. This may prevent the void-fillermaterial 112 from leaking into the environment surrounding the streamercable 100 in the event of a tear or other failure of the outer skin 102.

The void-filler material 112 may be coupled to the sensors 108. Couplingmay include placing the void-filler material 112 and the sensors 108 insufficient contact such that signals propagating through the void-fillermaterial 112 are received by the sensors 108. The signals may includeacoustic signals, thermal signals, pressure signals, etc. It can beappreciated that coupling may be enhanced by placing the void-fillermaterial 112 in direct physical contact with the sensors 108, and/orwith active surfaces 120 of the sensors 108. In various embodiments,this may be accomplished by filling the streamer cable with liquidmaterial that is then solidified around the sensor. It can beappreciated that this method may easily accommodate many sensor 108configurations, sizes, shapes, etc. It may also facilitate encapsulatingthe sensors 108 with void-filler material 112, e.g. positioning thevoid-filler material 112 to substantially surround or encapsulate atleast one active surface 120 of the sensors 108.

The void-filler material 112 may be made of any suitable solid materialthat couples incident signals, such as acoustic signals, to the sensors108 without also coupling excessive noise. Suitable void-fillermaterials 112 may be essentially incompressible and suitably compliant.An essentially incompressible material, for example, may undergo aminimal change in volume when subjected to a change in pressure.Therefore, an essentially incompressible void-filler material 112 maycouple pressure changes, for example, due to acoustic waves, to thesensors 108 rather than absorbing the pressure changes with a change involume. An essentially incompressible material may be characterized by arelatively high bulk modulus similar, for example, to that of kerosene.

A suitably compliant material may not couple excessive shear noise tothe sensors 108. Materials with a low compliance may not deformappreciably in response to shear energy. Therefore, shear energyincident on a low compliance material may be coupled through thematerial, for example, to a sensor 108. It can be appreciated that solidmaterials are generally of a lower compliance than liquid materials,such as kerosene. Nonetheless, a solid void-filler material 112 may bechosen with a high enough compliance that the level of shear noisecoupled to the sensors 108 is low enough for the streamer cable 100 tobe useful in seismic survey and other applications. In certainembodiments, it may be advantageous to choose a solid void-fillermaterial 112 with a compliance such that the level of shear noisecoupled to the sensors 108 is below the noise floor generated by otherambient signals in the ocean or other body of water. Other applications,however, favor a more rigid, less compliant void-filler material 112,even at the expense of slightly increased noise.

Examples of suitable solid materials for void-filler materials 112 mayinclude polymers, such as, for example, polymer gels, cross-linkedpolymers, thermoset polymers, thermoplastic polymers, photopolymers,multi-component resins, etc. The polymers may be homopolymers,copolymers, graft polymers, block copolymers, random copolymers or anyother polymer topology. Specific polymers that may be used invoid-filler material 112, alone or in combination, may include polymersprepared from isoprene, styrene, ethylene, propylene, butylene,urethanes, butadiene, acrylates, or derivations of such monomers. Incertain embodiments, void-filler may comprise a thermoplastic rubberincluding a series of hydrogenated styrenic block copolymers.

In various embodiments, solid void-filler material 112 may be installedinto streamer cables 100 designed to include the solid void-fillermaterial 112. It is also important to note that streamer cables 100 thatwere originally configured as liquid-filled streamer cables may beretrofitted to include the solid void-filler material 112 of the presentinvention for at least the reason that the solid void-filler material112, or constituent parts thereof, may be added to the streamer cable inat least a partially liquid state. This allows the void filler material112 to flow around the sensors and other components. Void-fillermaterial 112 may be introduced into either a new-design streamer cableor a streamer cable configured as a liquid-filled streamer cableaccording to various methods, for example, those set out below.

The void-filler material 112 or constituent parts thereof, may beintroduced into the streamer cable 100 in a liquid state and then curedto a solid state. In various embodiments, a void-filler material 112 maybe considered to be in a solid state when at least a portion of thematerial displays characteristics similar to those of a crystallinesolid. For a detailed discussion of the physical states of a polymer,see George Odian, Principles of Polymerization, 24-33 (John Wiley &Sons, Inc.) (1991), which is incorporated herein by reference. Invarious embodiments, the void-filler material 112 may be made ofmaterials other than polymers.

FIG. 2 is a flowchart of a process flow 200 for installing a void-fillermaterial 112 into a streamer cable 100 according to various embodimentsof the present invention. At step 202, constituent parts of thevoid-filler material 112 may be mixed together. The constituent partsmay include, for example, the components of a multi-component resinand/or a gel concentrate. The constituent parts may also include one ormore property modifying agents. Property modifying agents may include,for example, plasticizers and tackifiers. A plasticizer may affect, forexample, the compliance, density, buoyancy, overall weight, etc. of thevoid-filler material 112. A tackifier may affect, for example, theelasticity, etc. of the void-filler material 112. The constituent partsmay also include other additives including, for example, oil. In variousembodiments, the mixture of constituent parts may be heated.

At step 204, the constituent parts may be pumped into the streamer cable100. The constituent parts may be in a liquid state to facilitatepumping. At step 206, the constituent parts may be subjected to curingenergy. Curing energy may cause the constituent parts to cure into asolid state having favorable properties as a void-filler material 112.Curing energy may be, for example, in the form of heat energy, or lightenergy, such as ultraviolet light. Also, curing energy may be in theform of chemical energy provided by introducing a reactive agent, or across-linking agent to the constituent parts. The curing energy maycause, for example, one or more chemical reactions between one or moreof the constituent parts. In various embodiments, the one or morechemical reactions may cross-link the molecules of the void-fillermaterial 112. In embodiments where the constituent parts were heatedprior to being pumped into the streamer cable 100, curing may bealternatively facilitated by cooling the constituent parts within thestreamer cable 100.

In various embodiments, curing reactions may be made insensitive tomoisture and other environmental factors. For example, variousconstituent parts may react more readily with water than with the otherconstituent parts. When only a small amount of a water-sensitiveconstituent part is required, the entire quantity of the constituentpart provided may be consumed in a reaction with water or water vapor inthe environment, leaving none for curing reactions. This problem may beovercome by providing a large enough quantity of water-sensitiveconstituent parts to allow a reaction with water in the environment aswell as sufficient reactions with the other constituent parts in thecuring reactions.

FIG. 3 is a flowchart of an additional process flow 300 for installing avoid-filler material 112 into a streamer cable 100 according to variousembodiments of the present invention. Again, the streamer cable 100 maybe a new-design cable or a cable configured as a liquid-filled streamercable being retrofitted with a solid void-filler material 112 accordingto the present invention.

At step 302, an additive may be pumped into the streamer cable 100. Theadditive may be any constituent part of the void-filler material 112,and may constitute various percentages of the completed void-fillermaterial 112 by weight, volume, etc. For example, in variousembodiments, the additive may make up more than 50% of the void-fillermaterial 112 by weight, volume, etc. Additives may include, for example,oil, water, other solvents, and/or property modifying agents such astackifiers and plasticizers. Additives, for example, oil additives, maybe chosen for their compatibility with the void-filler material 112 andtheir overall density. Examples of oil additives may include oilhot-melts such as isomerized oils, iso parafins, α-olefins naphthenicoils, and/or other proprietary streamer oils, etc.

At step 304, the streamer cable and additive may be heated, for example,above the solidification temperature of the final void-filler material112. The solidification temperature of the void-filler material 112 maybe the temperature at which the void-filler material 112 transitions toor from a solid state. In various embodiments, the heating may beaccomplished by immersing the streamer cable 100, constituent parts ofthe void-filler material 112, and equipment used to handle the cable andconstituent parts, such as pumps, reservoirs, etc., in a hot water bath.

At step 306, gel concentrate may be introduced into the streamer cable.In some embodiments, the gel concentrate may be introduced by connectingthe streamer cable 100 containing the additive to a reservoir containingthe gel concentrate, for example, by opening a valve. The gelconcentrate in the reservoir may be in a liquid state as a result ofheating the reservoir above the solidification temperature at step 304.The additive may be circulated through the streamer cable 100 and thereservoir until a desired concentration of the gel concentrate ispresent in the streamer cable 100.

In other embodiments, gel concentrate may be introduced into thestreamer cable 100 by other means. For example, extruded strands ofsolid gel concentrate may be included in the streamer cable 100. Theextruded strands may be woven into strength members 104 or throughcavities 118, 124, 116, of bulkheads 106. In some embodiments, injectionmolded capsules or other shapes of gel concentrate may be included inthe streamer cable during its initial manufacture. It can be appreciatedthat upon the heating of the streamer cable 100 and additive at step304, gel concentrate contained in extruded strands and/or other solidcapsules or shapes may liquefy. The now-liquid gel concentrate may bedispersed in the streamer cable to a desired and/or uniform consistencyaccording to methods known in the art including, for example, fluidcirculation, agitation, etc.

When a desired concentration is reached, the additive and gelconcentrate may be cured or otherwise solidified at step 308. The curingmay involve, for example, subjecting the cable to curing energy, orcooling the streamer cable 100 and void-filler material 112 below thesolidification temperature of the void-filler material 112.

In order to facilitate maintenance of a streamer cable 100, void-fillermaterial 112 may be capable of transitioning from a solid state to aliquid state on the application of energy. For example, the void-fillermaterial 112 may be a thermoplastic polymer that transitions from asolid state to a liquid state at a solidification temperature. Invarious embodiments, the solidification temperature may be chosen abovethe highest expected operating, handling, and storage temperature of thestreamer cable 100. For example, the void-filler material 112 may have asolidification temperature between 60° and 100° centigrade. In variousembodiments, the solidification temperature of the void-filler material112 may be between 70° and 80° centigrade. Transitioning the void-fillermaterial 112 from a solid to a liquid may facilitate maintenance of thestreamer cable 100 by allowing the removal of at least a portion of thevoid-filler material 112.

FIG. 4 is a flowchart of a process flow 400 for performing maintenanceon a streamer cable 100 containing void-filler material 112 according tovarious embodiments of the present invention. At step 402, transitionenergy may be applied to the streamer cable 100, causing the void-fillermaterial 112 to transition from a solid to a liquid. For example, if thevoid-filler material 112 is a thermoplastic polymer, the energy maycause the temperature of the void-filler material 112 to rise above asolidification temperature. In some embodiments, transition energy maybe applied by placing the streamer cable 100 in a hot water bath. Atstep 404, all or a portion of the now-liquid void-filler material 112may be drained or pumped from the streamer cable 100. In someembodiments, the outer skin 102 of the streamer cable may be removedprior to applying transition energy. This may obviate the need to drainthe streamer cable 100 at step 404.

After the void-filler material 112 has been removed, a maintenanceoperation may be performed on the streamer cable 100 at step 406. Amaintenance operation may include, for example, fixing or replacing acomponent of the streamer cable 100, or simply replacing the void-fillermaterial 112.

In various embodiments, the void-filler material 112 may be chosen withadditional properties to increase its quality for use in specificapplications of a streamer cable 100. For example, the mobility, wavetransmission properties, density, elasticity, coefficient of volumetricthermal expansion, flashpoint, etc. of the void-filler material 112 maybe optimized to increase its usefulness.

A void-filler material 112 with appropriate mobility may enhance thesignals received by the streamer cable 100 by reducing noise. If thevoid-filler material 112 is overly mobile, the streamer cable 100 maytransmit bulge waves in response to forces incident on the streamercable 100 due to the motion of the cable and the tow vessel. Bulge wavespropagated in a streamer cable 100 may be coupled to the sensors 108,causing noise in the information generated by the sensors 108 or othercomponents. A particular streamer cable 100 may facilitate thepropagation of bulge waves only at certain frequency modes. Thefrequencies of the modes may depend on the mobility of the void-fillermaterial 112 and the elasticity of the outer skin 102. Acoustic noisedue to bulge waves may be minimized by choosing the mobility of thevoid-filler material 112 and the elasticity of the outer skin 102 suchthat none of the frequency modes of the streamer cable 100 fall withinthe signal frequencies to be measured by the streamer cable 100.

Wave transmission properties of the void-filler material 112 may beconsidered to ensure effective coupling, for example, when the streamercable 100 is used in a high-frequency application, such as militarysurveillance. The void-filler material 112 may be chosen with acousticimpedance close to that of the water outside the cable. Acousticimpedance is a measure of the ease with which acoustic energy maypropagate through a material. Choosing the void-filler material 112 withacoustic impedance similar to that of the outside water may allow agreater percentage of high frequency acoustic energy incident on thestreamer cable 100 to be coupled to the sensors 108 rather thanreflected. Accordingly, the void-filler material 112 may have anacoustic impedance between 1 and 2 mega-Rayls or about 1.5 mega-Rayls.

The void-filler material 112 may be chosen with a density to affect thedensity, and thus the buoyancy, of the streamer cable 100. It may bedesirable for a streamer cable 100 to have a density roughly equal tothat of seawater, e.g. neutral buoyancy, to facilitate operation atvarious depths. In various embodiments, the streamer cable 100, absentthe void-filler material 112, may have a density greater than that ofseawater. In that case, the void-filler material 112 may be chosen witha density less than that of seawater to make the overall density of thestreamer cable roughly equal to that of seawater. In variousembodiments, the density of the void-filler material 112 may bemanipulated by embedding solid filler units of varying densities withinthe void-filler material 112. For example, if the density of thevoid-filler material 112 is to be lowered, then filler units withrelatively low densities may be embedded, such as microbeads or foams.

Also, in various embodiments, a void-filler material 112 with a highelasticity may be chosen. A void-filler material with a high elasticitymay be more likely to resume its original shape after being deformed bystress. Thus an elastic void-filler material 112 may be, for example,more likely to remain in the streamer cable 100 in the event of afailure of the outer skin 102.

The void-filler material 112 may be chosen with properties that enhancethe streamer cable's 100 consistency of performance over an expectedrange of operating temperatures. A typical streamer cable 100 mayoperate in ambient water temperatures between −5° and 40° centigrade,and may be stored and handled in temperatures between −20° centigradeand 60° centigrade. It can be appreciated that should the compliance,compressibility, mobility, etc. of the void-filler 112 change, signalquality may not remain consistent. As such, it may be desirable tochoose a void-filler material 112 whose properties remain constant, orat least allow the streamer cable 100 to remain operative, over theexpected ambient water temperature range, or even over the entireexpected storage and handling temperature range.

In certain embodiments, for example when the void-filler material 112includes a polymer, choosing a material with an appropriate crystallinemelting temperature and glass transition temperature may enhance itsconsistency. For example, a material may be chosen with a crystallinemelting temperature above the highest expected operating temperature ofthe streamer cable 100, for example 60° centigrade, and a glasstransition temperature below the lowest expecting operating temperature,for example, −20° centigrade.

In certain embodiments, output consistency may also be enhanced bychoosing a void-filler material 112 with a relatively small coefficientof volumetric thermal expansion, for example less than 0.002 per degreecentigrade. In some embodiments, the coefficient of volumetric thermalexpansion of the void-filler material 112 may be 0.001 per degreecentigrade. It can be appreciated that excessive changes in thevoid-filler material's 112 volume may cause unwanted changes inbuoyancy. Therefore, it may be desirable to select a void-fillermaterial 112 with a low coefficient of volumetric thermal expansion.

The flashpoint of the void-filler material 112 may affect how the gelcan be shipped. Some shipping companies and/or regulatory bodies requirespecial accommodations, and additional expense, to ship materials with aflashpoint below a certain threshold. For example, some shippingcompanies will not ship a material with a flashpoint below 77°centigrade without special accommodations. As such, it may be desirableto choose the void-filler material 112 with a flashpoint above 77°centigrade. In various embodiments, the void-filler material 112 mayhave a flashpoint of between 77° and 150° centigrade.

It is to be understood that the present description illustrates thoseaspects of the invention relevant to a clear understanding of theinvention. Certain aspects of the invention that would be apparent tothose of ordinary skill in the art and that, therefore, would notfacilitate a better understanding of the invention, such as for example,various spacers, connectors, etc. and other components of streamercables, have not been presented in order to simplify the presentdescription. Although embodiments of the present invention have beendescribed, one of ordinary skill in the art will, upon considering theforegoing description, recognize that many modifications and variationsof the invention may be employed. All such variations and modificationsof the invention are intended to be covered by the foregoing descriptionand the following claims.

1-53. (canceled)
 54. A method of performing maintenance on a streamercable, the streamer cable comprising: an outer skin; at least one sensorpositioned within the outer skin; and a void-filler material positionedbetween the outer skin and the at least one sensor, wherein thevoid-filler material is coupled to the at least one sensor, the methodcomprising: changing the state of the void-filler material from a solidstate to a liquid state; removing at least a portion of the outer skin;and removing a portion of the void-filler material from the streamercable while the void-filler material is in the liquid state.
 55. Themethod of claim 54, wherein the changing the state of the void-fillermaterial comprises heating the streamer cable.
 56. The method of claim55, wherein the heating comprises immersing the streamer cable in a hotwater bath.
 57. The method of claim 54, further comprising performing amaintenance operation on the streamer cable. 58-70. (canceled)
 71. Themethod of claim 54, wherein the void-filler material comprises athermoplastic polymer.
 72. The method of claim 54, wherein thevoid-filler material has a solidification temperature between 60° and100° centigrade.
 73. The method of claim 54, wherein the void-fillermaterial has a solidification temperature between 70° and 80°centigrade.
 74. The method of claim 54, wherein the removing at least aportion of the outer skin is performed before the changing the state ofthe void-filler material.